Tone correcting circuit and hue correcting circuit

ABSTRACT

There are provided hue detecting means for detecting a hue component for each pixel from a first color difference signal R−Y and a second color difference signal B−Y, and gain controlling means for controlling for each pixel a gain for arbitrarily selected one of or an arbitrary combination of a luminance signal, a first color difference signal R−Y, and a second color difference signal B−Y depending on the detected hue component for each pixel.

TECHNICAL FIELD

The present invention relates to a tone correcting circuit, a huecorrecting circuit, and a color correcting circuit.

BACKGROUND ART

FIG. 1 illustrates the configuration of a conventional signal processingcircuit in a single plate-type CCD color camera.

A first 1H delay circuit 1 generates a video signal obtained by delayingan input video signal (a CCD output signal) by 1H (one horizontalperiod). A second 1H delay circuit 2 generates a video signal obtainedby further delaying by 1H the video signal delayed by 1H.

The input video signal, the video signal delayed by 1H, and the signaldelayed by 2H are fed to a YC separating circuit 3. A luminance signalYh, a vertical contour signal Vap, a G signal, an R signal, and a Bsignal are outputted from the YC separating circuit 3.

The luminance signal Yh and the vertical contour signal Vap are fed to aY process circuit 4, are subjected to predetermined luminance signalprocessing, and are then outputted as a luminance signal Yout.

The G signal, the R signal, and the B signal are fed to a colordifference matrix circuit 5. The color difference matrix circuit 5comprises four adders 11, 12, 13, and 14, four multipliers 21, 22, 23,and 24, and a color difference matrix coefficient register 25 for givinga multiplication coefficient to each of the multipliers 21, 22, 23, and24. The multiplication coefficient given to each of the multipliers 21,22, 23, and 24 is set in the color difference matrix coefficientregister 25 by a CPU 7.

Letting K_(RRY), K_(RBY), K_(BRY), and K_(BBY) be respectively themultiplication coefficients given to the multipliers 21, 22, 23, and 24,the color difference matrix circuit 5 performs an operation expressed bythe following equation (1), to generate color difference signals (R−Y)and (B−Y).R−Y=K _(RRY)(R−G)+K _(BRY)(B−G)B−Y=K _(RBY)(R−G)+K _(BBY)(B−G)  (1)

The color difference signals (R−Y) and (B−Y) obtained by the colordifference matrix circuit 5 are fed to a color encoding circuit 6.

In the color encoding circuit 6, two color carriers between which thereis a phase difference of 90 degrees are respectively modulated by thecolor difference signals (R−Y) and (B−Y), and are synthesized, togenerate a chrominance signal Cout.

In the above-mentioned circuit, the tone of a video output can beadjusted by changing the coefficients K_(RRY), K_(RBY), K_(BRY), andK_(BBY) in the color difference matrix circuit 5. That is, a gain in anR−Y direction, a hue (HUE) corresponding to a B−Y axis, a hue (HUE)corresponding to an R−Y axis, and a gain in a B−Y direction arerespectively adjusted by the coefficients K_(RRY), K_(BRY), K_(RBY), andK_(BBY), as shown in FIGS. 2 a, 2 b, 2 c, and 2 d.

Meanwhile, in the case of the single plate type CCD color camera, acolor filter is arranged on a front surface of a CCD. Particularly whena complementary color filter is used as the color filter, it isdifficult to change the spectral-response characteristics of Ye, Mg, Cy,and G color filters to ideal characteristics. Accordingly, a colordifferent from the inherent color is reproduced.

For example, green-based colors are not easily obtained, blue-basedcolors are predominantly obtained, and red-based colors are shifted in amagenta direction. It is difficult to adjust such degradation of colorreproducibility only by the coefficients K_(RRY), K_(RBY), K_(BRY), andK_(BBY) in the color difference matrix circuit 5. The reason for this isthat in a case where green-based colors are insufficient, for example,when the coefficient K_(RRY) is increased, green can be heightened,while cyan, red, and magenta are also similarly heightened.

An object of the present invention is to provide a tone correctingcircuit capable of correcting a tone only for an arbitrary hue.

Another object of the present invention is to provide a hue correctingcircuit capable of correcting a hue only for an arbitrary hue.

Still another object of the present invention is to provide a colorcorrecting circuit capable of correcting a color only for a hue withinan arbitrary range out of all hue ranges.

DISCLOSURE OF INVENTION

A tone correcting circuit according to the present invention ischaracterized by comprising hue detecting means for detecting a huecomponent for each pixel from a first color difference signal R−Y and asecond color difference signal B−Y; and gain controlling means forcontrolling for each pixel a gain for arbitrarily selected one of or anarbitrary combination of a luminance signal, a first color differencesignal R−Y, and a second color difference signal B−Y depending on thedetected hue component for each pixel, thereby correcting a tone onlyfor an arbitrary hue.

A gain is set for each hue. An example of the gain controlling means isone comprising gain calculating means for calculating for each pixel thegain corresponding to the hue component for each pixel detected by thehue detecting means on the basis of the set gain for each hue, and meansfor providing for each pixel the gain for the pixel calculated by thegain calculating means as the gain for arbitrarily selected one of orthe arbitrary combination of the luminance signal, the first colordifference signal R−Y, and the second color difference signal B−Y.

An example of the hue detecting means is one comprising a first bitshift circuit to which the first color difference signal (R−Y) isinputted, a second bit shift circuit to which a second color differencesignal (B−Y) is inputted, and means for outputting for each pixel huevalues corresponding to output values of both the bit shift circuits ashue components on the basis of a look-up table, each of the bit shiftcircuits cutting the number of bits composing an n-bit input signal to mwhich is smaller than n, cutting, when at least the respective uppermostbits in the color difference signals are both zero, the upper x bits ineach of the color difference signals, letting x be the smaller one ofthe number of bits, out of the bits from the uppermost bit to the(m+1)-th bit in one of the color difference signals, which arecontinuously zero from the uppermost bit and the number of bits, out ofthe bits from the uppermost bit to the (m+1)-th bit in the other colordifference signal, which are continuously zero from the uppermost bit,and further cutting the lower (n−m−x) bits in each of the colordifference signals when x is smaller than (n−m).

A hue correcting circuit according to the present invention ischaracterized by comprising hue detecting means for detecting a huecomponent for each pixel from a first color difference signal R−Y and asecond color difference signal B−Y; first offset providing means forproviding an offset for each pixel to the first color difference signalR−Y depending on the detected hue component for each pixel; and secondoffset providing means for providing an offset for each pixel to thesecond color difference signal B−Y, thereby correcting a hue only for anarbitrary hue.

An offset is set for each hue. An example of each of the offsetproviding means is one comprising saturation detecting means fordetecting saturation for each pixel from the first color differencesignal R−Y and the second color difference signal B−Y, offsetcalculating means for calculating for each pixel an offset correspondingto the hue component for each pixel detected by the hue detecting meanson the basis of the set offset for each hue, offset producing means formultiplying the offset for each pixel calculated by the offsetcalculating means by the saturation of the corresponding pixel detectedby the saturation detecting means, to produce for each pixel the offsetcorresponding to the saturation, and means for providing for each pixelthe offset for each pixel produced by the offset producing means to thecolor difference signal.

An example of the hue detecting means is one comprising a first bitshift circuit to which the first color difference signal (R−Y) isinputted, a second bit shift circuit to which a second color differencesignal (B−Y) is inputted, and means for outputting for each pixel huevalues corresponding to output values of both the bit shift circuits ashue components on the basis of a look-up table, each of the bit shiftcircuits cutting the number of bits composing an n-bit input signal to mwhich is smaller than n, cutting, when at least the respective uppermostbits in the color difference signals are both zero, the upper x bits ineach of the color difference signals, letting x be the smaller one ofthe number of bits, out of the bits from the uppermost bit to the(m+1)-th bit in one of the color difference signals, which arecontinuously zero from the uppermost bit and the number of bits, out ofthe bits from the uppermost bit to the (m+1)-th bit in the other colordifference signal, which are continuously zero from the uppermost bit,and further cutting the lower (n−m−x) bits in each of the colordifference signals when x is smaller than (n−m).

A first color correcting circuit according to the present invention ischaracterized in that within a color difference signal plane, the rangeof a hue is divided into a plurality of regions by at least two divisionaxes passing through the origin, and by comprising judging means forjudging, on the basis of input color difference signals R−Y and B−Y, towhich of the regions the hue of the input color difference signalbelongs, and color difference signal converting means for subjecting theinput color difference signal whose hue is judged to belong to thepredetermined region to color difference signal conversion processing,the color difference signal converting means comprising coefficientcalculating means for calculating, in a case where a position vector ofthe input color difference signal whose hue is judged to belong to thepredetermined region is decomposed into vector components correspondingto the two adjacent division axes, the coefficient of each of the vectorcomponents, and means for respectively primarily converting the vectorscorresponding to the two division axes by a transform matrix previouslyset, to convert the input color difference signal on the basis of thevectors corresponding to the two axes after the primary conversion andthe coefficients calculated by the coefficient calculation means.

A second color correcting circuit according to the present invention ischaracterized in that within a color difference signal plane, the rangeof a hue is divided into a plurality of regions by at least two divisionaxes passing through the origin, and by comprising judging means forjudging, on the basis of input color difference signals R−Y and B−Y, towhich of the regions the hue of the input color difference signalbelongs, and color difference signal converting means for subjecting theinput color difference signal whose hue is judged to belong to thepredetermined region to color difference signal conversion processing,the color difference signal converting means comprising coefficientcalculating means for calculating, in a case where it is assumed that aposition vector of the input color difference signal whose hue is judgedto belong to the predetermined region is decomposed into vectorcomponents corresponding to the two adjacent division axes, thecoefficient of each of the vector components, and means for convertingthe input color difference signal on the basis of vectors correspondingto the two axes after the conversion, which have been previously set forthe vector components corresponding to the two division axes and thecoefficients calculated by the coefficient calculating means.

The range of the hue is divided into six regions by three division axescomprising a Ye−B axis, a Cy−R axis, and an Mg−G axis within the colordifference signal plane. An example of the judging means is one forjudging to which of the regions the hue of the input color differencesignal belongs on the basis of the input color difference signals R−Yand B−Y.

An example of the judging means is one comprising means for operatingthe respective inner products of vectors respectively perpendicular tothe vectors corresponding to the division axes and the position vectorof the input color difference signal, and means for judging to which ofthe regions the hue of the input color difference signal belongs on thebasis of the respective signs of the inner products.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing the configuration of a conventionalsignal processing circuit in a single plate type CCD color camera.

FIGS. 2 a to 2 d are schematic views for explaining that the tone of avideo output can be adjusted by changing coefficients K_(RRY), K_(RBY),K_(BRY), and K_(BBY) in a color difference matrix circuit.

FIG. 3 is a block diagram showing the configuration of a signalprocessing circuit in a single plate type CCD color camera.

FIG. 4 is a block diagram showing the configuration of a tone and huecorrecting circuit.

FIG. 5 is a schematic view showing a hue value C_Phase calculated by ahue calculating circuit.

FIG. 6 is a block diagram showing the configuration of a hue calculatingcircuit.

FIG. 7 is a graph showing a gain for each hue value set in a gaincalculation register in a case where it is desired to emphasize onlygreen.

FIG. 8 is a schematic view showing that the saturation of green isincreased in a case where a gain for each hue value as shown in FIG. 7is set in a gain calculation register.

FIG. 9 is a graph showing an offset for each hue value set in eachoffset calculation register in a case where it is desired to correct thehue of green toward Ye.

FIG. 10 is a schematic view showing that the hue of green is correctedtoward Ye in a case where an offset for each hue value as shown in FIG.9 is set in an offset calculation register.

FIG. 11 is a block diagram showing the configuration of a colorcorrecting circuit.

FIG. 12 is a schematic view showing a color difference signal planewhere a color difference signal (B−Y) and a color difference signal(R−Y) are respectively used to enter the X-axis and the Y-axis.

FIG. 13 is a schematic view showing position vectors a, b, and c for B,R, and G colors and vectors a′, b′, and c′ perpendicular thereto.

FIG. 14 is a schematic view showing how a position vector p of an inputcolor difference signal is decomposed into vector components indirections corresponding to two axes adjacent to the position vector p.

FIG. 15 is a schematic view showing a color (a position vector p′) afterconversion.

FIG. 16 is a block diagram showing another example of a color correctingcircuit.

BEST MODE FOR CARRYING OUT THE INVENTION

Description is now made of embodiments in a case where the presentinvention is applied to a single plate type color camera.

[A] First Embodiment

Referring to FIGS. 3 to 10, a first embodiment of the present inventionwill be described.

FIG. 3 illustrates the configuration of a signal processing circuit in asingle plate type CCD color camera. In FIG. 3, the same components asthose shown in FIG. 1 are assigned the same reference numerals andhence, the description thereof is not repeated. In the signal processingcircuit, a tone and hue correcting circuit 100 is added to the signalprocessing circuit shown in FIG. 1.

FIG. 4 illustrates the configuration of the tone and hue correctingcircuit 100.

A luminance signal Y outputted from a Y process circuit 4 and colordifference signals (R−Y) and (B−Y) outputted from a color differencematrix circuit 5 are inputted to the tone and hue correcting circuit100.

The tone and hue correcting circuit 100 comprises a hue calculatingcircuit 101, a saturation calculating circuit 102 for calculatingsaturation on the basis of the color difference signals (R−Y) and (B−Y),a gain correcting circuit (a tone correcting circuit) 103, and a huecorrecting circuit 104.

The hue calculating circuit 101 calculates for each pixel a hue valueC_Phase, as shown in FIG. 5, on the basis of the color differencesignals (R−Y) and (B−Y). The hue value C_Phase is found as values 0.0 to4.0 corresponding to an angle centered at the origin on a colordifference signal plane, as shown in FIG. 5. Consequently, the hue valueC_Phase is a value corresponding to the ratio of the color differencesignals (R−Y)/(B−Y) (more specifically, tan⁻¹{(R−Y)/(B−Y)}).

The hue calculating circuit 101 comprises a first bit shift circuit 111to which the color difference signal (R−Y) is inputted, a second bitshift circuit 112 to which the color difference signal (B−Y) isinputted, and a ROM 113, as shown in FIG. 6.

The two bit shift circuits 111 and 112 are provided in order to cut thenumber of bits composing an 8-bit input signal to five. That is, each ofthe bit shift circuits 111 and 112 performs bit shifting, describedbelow.

(1) When the upper three bits in each of the color difference signals(R−Y) and (B−Y) are zero, the bit shifting is performed such that theupper three bits are cut.

(2) When the upper two bits in each of the color difference signals(R−Y) and (B−Y) are zero, the bit shifting is performed such that theupper two bits are cut, and the lower one bit is rounded down (cut).

(3) When the upper one bit in each of the color difference signals (R−Y)and (B−Y) is zero, the bit shifting is performed such that the upper onebit is cut, and the lower two bits are rounded down (cut).

(4) In a case which does not correspond to the foregoing items (1) to(3), the bit shifting is performed such that the lower three bits ineach of the color difference signals (R−Y) and (B−Y) are rounded down(cut).

The 5-bit color difference signal (R−Y) and the 5-bit color differencesignal (B−Y) which are inputted are inputted to the ROM 113. The ROM 113outputs for each pixel a hue value C_Phase corresponding to the valuesof the input color difference signals (R−Y) and (B−Y) on the basis of ahue conversion table previously stored.

The saturation calculating circuit 102 calculates for each pixelsaturation on the basis of the color difference signals (R−Y) and (B−Y).The saturation calculating circuit 102 calculates for each pixelsaturation corresponding to the magnitude of each of the input colordifference signals (R−Y) and (B−Y) on the basis of a saturationconversion table previously stored.

The gain correcting circuit 103 comprises a multiplier 121 for adjustingthe gain of the luminance signal Y, a multiplier 122 for adjusting thegain of the color difference signal (R−Y), a multiplier 123 foradjusting the gain of the color difference signal (B−Y), a gaincalculation register 124, and two selecting circuits (SEL) 125 and 126.

In the gain calculation register 124, a gain for each hue value is setby a user in order to adjust the saturation of a particular hue andadjust the lightness of the particular hue. That is, the gain is set atintervals of 0.25 for the hue values 0.0 to 4.0 in the gain calculationregister 124.

In cases such as a case where it is desired to only emphasize green (acase where it is desired to increase the concentration of green) and acase where it is desired to brighten only green, such gains for each huevalue that the gain against only the hue of green (the vicinity of thehue value 2.75) is increased are set in the gain calculation register124, as shown in FIG. 7.

The gain calculation register 124 calculates for each pixel a gaincorresponding to the hue value C_Phase sent from the hue calculatingcircuit 101, and outputs the calculated gain. Gains are set at intervalsof 0.25 for the hue values 0.0 to 4.0 in the gain calculation register124. When the hue value C_Phase sent from the hue calculating circuit101 is a value between the two hue values for which the gains arerespectively set, therefore, the gain calculation register 124 linearlyinterpolates the gains for the two hue values, thereby calculating thegain for the inputted hue value C_Phase and outputting the calculatedgain.

The gain calculated for each pixel by the gain calculation register 124is sent to the first selecting circuit 125 and the second selectingcircuit 126. The first selecting circuit 125 selects the gain or “1”calculated by the gain calculation register 124, and sends the selectedgain or “1” to the multipliers 122 and 123. The second selecting circuit126 selects the gain or “1” calculated by the gain calculation register124, and sends the selected gain or “1” to the multiplier 121.

When the concentration of the particular hue is adjusted, the firstselecting circuit 125 is controlled such that the gain calculated by thegain calculation register 124 is selected. When the brightness of theparticular hue is adjusted, the second selecting circuit 126 iscontrolled such that the gain calculated by the gain calculationregister 124 is selected.

In a case where such gains that the gain against only the hue of greenis increased are set, as shown in FIG. 7, in the gain calculationregister 124, for example, suppose a case where the gain calculated bythe gain calculation register 124 through the first selecting circuit125 is sent to the multipliers 122 and 123. In this case, the gains ofthe color difference signals (R−Y) and (B−Y) against the hue of greenare raised. Accordingly, the saturation of green is increased, as shownin FIG. 8.

Furthermore, when the gain calculated by the gain calculation register124 through the second selecting circuit 126 is sent to the multiplier121, the gain of the luminance signal Y against the hue of green israised. Accordingly, the lightness of green is increased.

The hue correcting circuit 104 comprises an R−Y offset calculationregister 131, a B−Y offset calculation register 132, a multiplier 133for multiplying saturation calculated by the saturation calculatingcircuit 102 by an offset outputted from the R−Y offset calculationregister 131, a multiplier 134 for multiplying the saturation calculatedby the saturation calculating circuit 102 by an offset outputted fromthe B−Y offset calculation register 132, an adder 135 for adding anoffset outputted from the multiplier 133 to the color difference signal(R−Y) outputted from the gain correcting circuit 103, and an adder 136for adding an offset outputted from the multiplier 134 to the colordifference signal (B−Y) outputted from the gain correcting circuit 103.

The offset for each hue value is set by the user, in order to correctthe hue for only the particular hue, in each of the R−Y offsetcalculation register 131 and the B−Y offset calculation register 132.That is, the offset is set at intervals of 0.25 against the hue values0.0 to 4.0 in each of the offset calculation registers 131 and 132.

In a case where it is desired to correct the hue of green toward Ye, forexample, the offset for each hue value, as shown in FIG. 9, is set ineach of the offset calculation registers 131 and 132. In FIG. 9, R−Yindicates the offset for each hue value set in the R−Y offsetcalculation register 131, and B−Y indicates the offset for each huevalue set in the B−Y offset calculation register 132.

Each of the offset calculation registers 131 and 132 calculates for eachpixel an offset corresponding to the hue value C_Phase sent from the huecalculating circuit 101, and outputs the calculated offset. Offsets areset at intervals of 0.25 for the hue values 0.0 to 4.0 in each of theoffset calculation registers 131 and 132. When the hue value C_Phasesent from the hue calculating circuit 101 is a value between the two huevalues for which the offsets are respectively set, therefore, each ofthe offset calculation registers 131 and 132 linearly interpolates theoffsets for the two hue values, thereby calculating the offset for theinputted hue value C_Phase and outputting the calculated offset.

The offset calculated for each pixel by the R−Y offset calculationregister 131 is sent to the multiplier 133, and is multiplied by thesaturation calculated by the saturation calculating circuit 102.Consequently, the R−Y offset corresponding to the saturation is obtainedfor each pixel. Similarly, the offset for each pixel calculated by theR−Y offset calculation register 132 is sent to the multiplier 134, andis multiplied by the saturation calculated by the saturation calculatingcircuit 102. Consequently, the B−Y offset corresponding to thesaturation is obtained for each pixel.

The R−Y offset outputted from the multiplier 133 is sent to the adder135, and is added to the color difference signal (R−Y) outputted fromthe gain correcting circuit 103. Similarly, the B−Y offset outputtedfrom the multiplier 134 is sent to the adder 136, and is added to thecolor difference signal (B−Y) outputted from the gain correction circuit103.

When an offset for correcting the hue of green toward Ye is set, asshown in FIG. 9, in each of the offset calculation registers 131 and132, for example, the offset is provided to the color difference signal(R−Y) corresponding to the hue of green such that the magnitude thereofis decreased, and the offset is provided to the color difference signal(B−Y) corresponding to the hue of green such that the magnitude thereofis increased. Consequently, the hue of green is moved toward Ye, asshown in FIG. 10.

Although in the above-mentioned first embodiment, description was madeof a case where the saturation, lightness, and hue are adjusted for thehue of green, it goes without saying that the saturation, lightness, andhue can be also similarly adjusted for another arbitrary hue.

Although in the above-mentioned first embodiment, description was madeof a case where the present invention is applied to the single platetype color camera, the present invention is also applicable to videodisplay devices such as a television receiver, a VTR, and a liquidcrystal projector.

According to the above-mentioned first embodiment, the tone can becorrected only for the arbitrary hue. Further, according to theabove-mentioned first embodiment, the hue can be corrected only for thearbitrary hue.

[B] Description of Second Embodiment

Referring to FIGS. 11 to 15, a second embodiment of the presentinvention will be described.

[1] Description of Configuration of Color Correcting Circuit

FIG. 11 illustrates the configuration of a color collecting circuit in asingle plate type color camera.

The color correcting circuit is provided in the succeeding stage of thecolor difference matrix circuit 5 shown in FIG. 1. The color correctingcircuit comprises a color region judging unit 201, a color selectingunit 202, a vector decomposing unit 203, a first vector converting unit204, a second vector converting unit 205, and a vector synthesizing unit206.

[2] Description of Color Region Judging Unit 201

Description is made of color region judgment processing by the colorregion judging unit 201.

Input color difference signals (B−Y) and (R−Y) are inputted to the colorregion judging unit 201, and coordinate values on a color differencesignal plane of R, G, and B colors are inputted thereto.

FIG. 12 illustrates a color difference signal plane where the colordifference signal (B−Y) and the color difference signal (R−Y) arerespectively used to enter the X-axis and the Y-axis. Within the colordifference signal plane, six triangular regions each formed by theorigin and two adjacent ones of the vertexes Mg, R, Ye, G, Cy, and B ofa hexagon are respectively taken as S1, S2, S3, S4, S5, and S6.

In other words, within the color difference signal plane, the range of ahue is divided into six regions S1 to S6 by three division axes, i.e., aYe-B axis, a Cy-R axis, and an Mg-G axis.

The color region judging unit 201 judges for each pixel to which of theregions S1 to S6 the hue of the input color difference signal belongs onthe basis of the color difference signals (R−Y) and (B−Y) inputted foreach pixel. The judging method will be described.

Letting a, b, and c be respectively position vectors for B, R and Gcolors, as shown in FIG. 13, the vectors a, b, and c can be expressed bythe following equation (2) using the coordinate values (ax, ay), (bx,by), and (cx, cy) of B, R, and G colors:a=(ax,ay)b=(bx,by)c=(cx,cy)  (2)

Letting a′, b′, and c′ be vectors obtained by rotating the vectors a, b,and c by 90 degrees in a counterclockwise direction, the vectors a′, b′,and c′ are expressed by the following equation (3):a′=(−ay,ax)b′=(−by,bx)c′=(−cy,cx)  (3)

Let p be a position vector of the input color difference signal. Therespective inner products of the position vector p of the input colordifference signal and the vectors a′, b′, and c′ are operated on thebasis of the following equation (4):p·a′=px·(−ay)+py·axp·b′=px·(−by)+py·bxp·c′=px·(−cy)+py·cx  (4)

It is judged to which of the regions S1 to S6 the hue of the input colordifference signal belongs on the basis of the respective signs of theinner products and a region judgment table shown in Table 1.

TABLE 1 S1 S2 S3 S4 S5 S6 S7 S8 a′ + + + − − − + − b′ − − + + + − + −c′ + − − − + + + −

In Table 1, S7 indicates the origin. S8 indicates that there is noregion. Further, in Table 1, + includes zero.

[3] Description of Color Selecting Unit 202

The results of the judgment by the color region judging unit 201 areinputted to the color selecting unit 202, and the coordinate values onthe color difference signal plane of R, G, B, Mg, Cy, and Ye colors anda transform matrix for one, corresponding to a region where the color ischanged, of the R, G, B, Mg, Cy, and Ye axes are inputted thereto. Here,description is made of a case where the color in a region S1 is changed.Consequently, transform matrices corresponding to the two axes B and Mgfor defining the region S1 are inputted.

With respect to the input color difference signal whose hue is judged tobe within the region S1, the color selecting unit 202 respectivelyselects and outputs the coordinate values of the colors B and Mgcorresponding to the two axes (the first axis and the second axis) fordefining the region S1 and the transform matrices corresponding to theaxes.

The coordinate values of the colors B and Mg outputted from the colorselecting unit 202 are sent to the vector decomposing unit 203. Thecoordinate value of the color B outputted from the color selecting unit202 and the transform matrix corresponding to the B axis are sent to thefirst vector converting unit 204. The coordinate value of the color Mgoutputted from the color selecting unit 202 and the transform matrixcorresponding to the Mg axis are sent to the second vector convertingunit 205.

[4] Description of Vector Decomposing Unit 203

It is assumed that the position vector p of the input color differencesignal whose hue is judged to be within the region S1 is decomposed intovector components in directions (a and b directions) of the two axes(two axes adjacent to the position vector p) for designating the regionS1. That is, it is assumed that the position vector p of the input colordifference signal is decomposed into vector components corresponding toan axis in a direction of c and an axis in a direction a, as shown inFIG. 14. As the vectors corresponding to the two axes, vectors directedtoward the six vertexes Mg, R, Ye, G, Cy, and B of the hexagon from theorigin are used.

Letting t be the vector directed toward Mg from the origin (in theopposite direction to c), and letting s be the vector directed toward Bfrom the origin (in the same direction as a), as shown in FIG. 14, p isexpressed by the following equation (5):p=α·s+β·t  (5)

α and β are coefficients, where α, β≧0.

Letting px, sx, tx be respectively x components of p, s, and t, andletting py, sy, and ty be respectively y components of p, s, and t, px(=an input color difference signal (B−Y) ) and py (=an input colordifference signal (R−Y)) are expressed by the following equation (6):px=α·sx+β·txpy=α·sy+β·ty  (6)

Consequently, the coefficients α and β are found by the followingequation (7):α=(ty·px−tx·py)/(sx·ty−sy·tx)β=(−sy·px+sx·py)/(sx·ty−sy·tx)  (7)

The vector decomposing unit 203 calculates sx, sy, tx, and ty from thecoordinate values of the colors B and Mg sent from the color selectingunit 202. Further, the vector decomposing unit 203 calculates px and pyfrom the input color difference signal. The coefficients α and β arefound on the basis of the foregoing equation (7). The coefficients α andβ found by the vector decomposing unit 203 are sent to the vectorsynthesizing unit 206.

[5] Description of First Vector Converting Unit 204 and Second VectorConverting Unit 205

Before describing the operations of each of the vector converting units204 and 205, description is made of an idea for converting the color(the position vector p) of the input color difference signal will bedescribed.

In order to convert the color (the position vector p) of the input colordifference signal, the two axes s and t shown in FIG. 14 are firstprimarily converted by transform matrices S and T respectively expressedby the following equations (8) and (9):

$\begin{matrix}{S = {\begin{matrix}{S11} & {S12} \\{S21} & {S22}\end{matrix}}} & (8) \\{T = {\begin{matrix}{T11} & {T12} \\{T21} & {T22}\end{matrix}}} & (9)\end{matrix}$

The coefficients in the transform matrices S and T are previously setdepending on the contents of the change in the hue in the region S1.Letting Ss and Tt be respectively s and t after the conversion, thecolor (the position vector p′) after the change is expressed by thefollowing equation (10):p′=α·Ss+β·Tt  (10)

Letting px′ be the component of p′ (the color difference signal (B−Y)after the change), and letting py′ be the y component of p′ (the colordifference signal (R−Y) after the change), px′ and py′ are found by thefollowing equation (11):px′=α·(S11·sx+S12·sy)+β·(T11·tx+T12·ty)py′=α·(S21·sx+S22·sy)+β·(T21·tx+T22·ty)  (11)

The first vector converting unit 204 calculates sx and sy on the basisof the coordinate value of the color B sent from the color selectingunit 202. (S11·sx+S12·sy)=X1 and (S21·sx+S22·sy)=Y1 in the foregoingequation (11) are calculated and outputted on the basis of sx and syobtained and the transform matrix S corresponding to the B axis sentfrom the color selecting unit 202.

The second vector converting unit 205 calculates tx and ty on the basisof the coordinate value of the color Mg sent from the color selectingunit 202. (T11·tx+T12·ty)=X2 and (T21·tx+T22·ty)=Y2 in the foregoingequation (11) are calculated and outputted on the basis of tx and tyobtained and the transform matrix T corresponding to the Mg axis sentfrom the color selecting unit 202.

X1 and Y1 calculated by the first vector converting unit 204 and X2 andY2 calculated by the second vector converting unit 205 are sent to thevector synthesizing unit 206.

[6] Description of Vector Synthesizing Unit 206

The vector synthesizing unit 206 calculates and outputs px′ (the colordifference signal (B−Y) after the change) and py′ (the color differencesignal (R−Y) after the change) on the basis of the coefficients α and βcalculated by the vector decomposing unit 203, X1 and Y1 calculated bythe first vector converting unit 204, and X2 and Y2 calculated by thesecond vector converting unit 205, and the foregoing equation (11).

The color (the position vector p′) after the conversion is as shown inFIG. 15, for example. In this example, the color in the region S1 iscorrected toward the region S2. That is, the color in the region S1 canbe changed by changing the coefficients in the transform matrices S andT. The color in the other region can be also similarly changed.

[C] Description of Third Embodiment

Referring to FIG. 16, a third embodiment of the present invention willbe described.

[1] Description of Characteristics of Third Embodiment

First, description is made of the characteristics of a third embodiment,that is, the difference from the above-mentioned second embodiment. Thethird embodiment is characterized in two points.

[1-1] Description of First Feature Point

In the above-mentioned second embodiment, the color region judging unit201 calculates the respective inner products of the position vector p ofthe input color difference signal and the vectors a′, b′, and c′, andjudges to which of the regions S1 to S6 the hue of the input colordifference signal belongs by the respective signs of the inner products.In this case, the inner products are expressed by the followingmathematical expression (12), as expressed by the foregoing equation(4):p·a′=px·(−ay)+py·axp·b′=px·(−by)+py·bxp·c′=px·(−cy)+py·cx  (12)

Furthermore, in the above-mentioned second embodiment, the positionvector p of the input color difference signal is decomposed into thevector components in the directions of the two axes (two axes adjacentto the position vector p) for defining the region including the vector p(S1 in the example shown in FIG. 14), as shown in FIG. 14.

In the case, letting s and t be respectively vectors corresponding tothe two axes, the position vector p indicates p=α·s+β·t, as expressed bythe foregoing equation (5). α and β are expressed by the followingequation (13), as expressed by the foregoing equation (7):α=(ty·px−tx·py)/(sx·ty−sy·tx)β=(−sy·px+sx·py)/(sx·ty−sy·tx)  (13)

As shown in FIG. 14, when the position vector p is in the region S1,sx=ax, sy=ay, tx=−cx, and ty=−cy. Accordingly, the numerator (α′) of αand the numerator (β′) of β in the foregoing equation (13) can bedeformed, as expressed by the following equation (14):α′={px·(−cy)−py·(−cx)}=p·c′β′={px·(−ay)+py·ax}=p·a′  (14)

Furthermore, the respective reciprocals K of the denominators of α and βin the foregoing equation (13) can be deformed, as expressed by thefollowing equation (15):K=1/{ax·(−cy)−ay·(−cx)}  (15)

The value of K is a constant determined for each of the regions S1 toS6.

In the third embodiment, the amount of operation processing of thenumerators α′ and β′ of α and β is reduced by utilizing the innerproduct calculated in region judgment, and the amount of operationprocessing of the denominators of α and β is reduced by using Kpreviously found for each of the regions.

[1-2] Description of Second Feature Point

In the above-mentioned second embodiment, when the position vector pshown in FIG. 14 is converted into a position vector p′ shown in FIG.15, vectors s and t corresponding to two axes with the position vector pinterposed therebetween are primarily converted using the transformmatrices S and T expressed by the equations (8) and (9).

In this case, the position vector p′ after the conversion satisfiesp′=α·Ss+β·Tt, as expressed by the foregoing equation (10). Further, xcomponents px′ and py′ of the position vector p′ after the conversionare expressed by the following equation (16), as expressed by theforegoing equation (11):

$\begin{matrix}\begin{matrix}\begin{matrix}{{px}^{\prime} = {{\alpha \cdot \left( {{{S11} \cdot {sx}} + {{S12} \cdot {sy}}} \right)} + {\beta \cdot \left( {{{T11} \cdot {tx}} + {{T12} \cdot {ty}}} \right)}}} \\{= {{\alpha \cdot {X1}} + {\beta \cdot {X2}}}} \\\;\end{matrix} \\\begin{matrix}{{py}^{\prime} = {{\alpha \cdot \left( {{{S21} \cdot {sx}} + {{S22} \cdot {sy}}} \right)} + {\beta \cdot \left( {{{T21} \cdot {tx}} + {{T22} \cdot {ty}}} \right)}}} \\{= {{\alpha \cdot {Y1}} + {\beta \cdot {Y2}}}} \\\;\end{matrix}\end{matrix} & (16)\end{matrix}$

In the third embodiment, the coordinates (corresponding to Ss and Tt)after the conversion of the two axes s and t with the position vector pinterposed therebetween are previously determined, thereby eliminatingthe necessity of a matrix operation for calculating X1, X2, Y1, and Y2.

That is, letting s′ and t′ be respectively the coordinates after theconversion of the two axes s and t with the position vector p interposedtherebetween, s′x be the x component of s′, s′y be the y component ofs′, t′x be the x component of t′, and t′y be the y component of t′, X1,X2, Y1, and Y2 are found by the following equation (17):X1=s′xX2=t′xY1=s′yY2=t′y  (17)

[2] Description of Configuration of Color Correcting Circuit in SinglePlate Type Color Camera

FIG. 16 illustrates the configuration of a color correcting circuit in asingle plate type color camera.

The color correcting circuit comprises a color region operating unit301, a α′ and β′ selecting unit 302 for producing α′ and β′, a Kselecting unit 303 for producing K, a coordinate selecting unit 304 forproducing X1, X2, Y1, and Y2, and a converted coordinate operating unit305.

[3] Description of Color Region Operating Unit 201

The color region operating unit 301 calculates the respective innerproducts of a position vector p of an input color difference signal andvectors a′, b′, and c′, and judges to which of regions S1 to S6 the hueof the input color difference signal belongs by the respective signs ofthe inner products, similarly to the color region judging unit 201 shownin FIG. 11.

The color region operating unit 301 outputs region information which isthe results of the region judgment, and outputs the inner product valuesp·a′, p·b′, and p·c′ of the position vector p used for the regionjudgment and the vectors a′, b′, and c′.

The region information outputted from the color region operating unit301 is fed to the α′ and β′ selecting unit 302, the K selecting unit303, and the coordinate selecting unit 304. The inner product valuesp·a′, p·b′, and p·c′ outputted from the color region operating unit 301are fed to the α′ and β′ selecting unit 302.

[4] Description of α′ and β′ Selecting Unit 302

The α′ and β′ selecting unit 302 outputs α′ and β′ on the basis of theregion information inputted from the color region operating unit 301 andthe inner product values p·a′, p·b′, and p·c′.

The relationship between the results of the region judgment representedby the region information and α′ and β′ outputted from the α′ and β′selecting unit 302 is shown in Table 2:

TABLE 2 α′ β′ region α′ β′ S1 α′ = px · (−cy) − py · (−cx) = p · c′ β′ =px · (−ay) + py · ax = p · a′ S2 α′ = px · by − py · bx = − p · b′ β′ =px · cy + py · (−cx) = −p · c′ S3 α′ = px · (−ay) − py · (−ax) = p · a′β′ = px · (−by) + py · bx = p · b′ S4 α′ = px · cy − py · cx = −p · c′β′ = px · ay + py · (−ax) = −p · a′ S5 α′ = px · (−by) − py · (−bx) = p· b′ β′ = px · (−cy) + py · cx = p · c′ S6 α′ = px · ay − py · ax = −p ·a′ β′ = px · by + py · (−bx) = −p · b′ S7 α′ = 0 β′ = 0 S8 α′ = 0 β′ = 0

[5] Description of K Selecting Unit 303

The K selecting unit 303 selects, out of the values of K previouslyfound for the regions S1 to S8, K corresponding to the regioninformation inputted from the color region operating unit 301, andoutputs the selected K.

The relationship between the results of the region judgment S1 to S8represented by the region information and K outputted from the Kselecting unit 303 is shown in Table 3.

TABLE 3 K region K S1$K = \frac{1}{{{ax} \cdot \left( {- {cy}} \right)} - {{ay} \cdot \left( {- {cx}} \right)}}$S2$K = \frac{1}{{\left( {- {cx}} \right) \cdot {by}} - {\left( {- {cy}} \right) \cdot {bx}}}$S3$K = \frac{1}{{{bx} \cdot \left( {- {ay}} \right)} - {{by} \cdot \left( {- {ax}} \right)}}$S4$K = \frac{1}{{\left( {- {ax}} \right) \cdot {cy}} - {\left( {- {ay}} \right) \cdot {cx}}}$S5$K = \frac{1}{{{cx} \cdot \left( {- {by}} \right)} - {{cy} \cdot \left( {- {bx}} \right)}}$S6$K = \frac{1}{{\left( {- {bx}} \right) \cdot {ay}} - {\left( {- {by}} \right) \cdot {ax}}}$S7 K = 0 S8 K = 0

[6] Description of Coordinate Selecting Unit 304

Coordinates after conversion corresponding to R, G, B, Mg, Cy, and Yeaxes taking the origin of a color difference signal plane as its basepoint are given to the coordinate selecting unit 304. The coordinateselecting unit 304 outputs X1, X2, Y1, and Y2 on the basis of thecoordinates after conversion corresponding to the two axes for defininga region represented by the region information inputted from the colorregion operating unit 301.

[7] Description of Converted Coordinate Operating Unit 305

The converted coordinate operating unit 305 finds the color (theposition vector p′) after conversion on the basis of α′ and β′ sent fromthe α′ and β′ selecting unit 302, K sent from the K selecting unit 303,and X1, X2, Y1, and Y2 sent from the coordinate selecting unit 304.

That is, α and β are first found on the basis of the following equation(18):α=Kα′β=Kβ′  (18)

px′ (a color difference signal (B−Y) after change) and py′ (a colordifference signal (R−Y) after change) are calculated and outputted onthe basis of the following equation (19):px′=α·X1+β·X2py′=α·Y1+β·Y2  (19)

Although in the above-mentioned second or third embodiment, descriptionwas made of a case where the present invention is applied to the singleplate type color camera, the present invention is also applicable tovideo display devices such as a television receiver, a VTR, and a liquidcrystal projector.

According to the above-mentioned second or third embodiment, it ispossible to correct, in all the hue ranges, a color only for the hue inthe arbitrary range.

1. A tone correcting circuit comprising: hue detecting means fordetecting a hue component for each pixel from a first color differencesignal R−Y and a second color difference signal B−Y; and gaincontrolling means for controlling for each pixel a gain for arbitrarilyselected one of or an arbitrary combination of a luminance signal, afirst color difference signal R−Y, and a second color difference signalB−Y depending on the detected hue component for each pixel, therebycorrecting a tone only for an arbitrary hue, wherein the hue detectingmeans comprises a first bit shift circuit to which the first colordifference signal (R−Y) is inputted, a second bit shift circuit to whicha second color difference signal (B−Y) is inputted, and means foroutputting for each pixel hue values corresponding to output values ofboth the bit shift circuits as hue components on the basis of a look-uptable, and each of the bit shift circuits cutting the number of bitscomposing an n-bit input signal to m which is smaller than n, cutting,when at least the respective uppermost bits in the color differencesignals are both zero, the upper x bits in each of the color differencesignals, letting x be the smaller one of the number of bits, out of thebits from the uppermost bit to the (m+1)-th bit in one of the colordifference signals, which are continuously zero from the uppermost bitand the number of bits, out of the bits from the uppermost bit to the(m+1)-th bit in the other color difference signal, which arecontinuously zero from the uppermost bit, and further cutting the lower(n−m−x) bits in each of the color difference signals when x is smallerthan (n−m).
 2. The tone correcting circuit according to claim 1, whereina gain is set for each hue, the gain controlling means comprising gaincalculating means for calculating for each pixel the gain correspondingto the hue component for each pixel detected by the hue detecting meanson the basis of the set gain for each hue, and means for providing foreach pixel the gain for the pixel calculated by the gain calculatingmeans as the gain for arbitrarily selected one of or the arbitrarycombination of the luminance signal, the first color difference signalR−Y, and the second color difference signal B−Y.
 3. A hue correctingcircuit comprising: hue detecting means for detecting a hue componentfor each pixel from a first color difference signal R−Y and a secondcolor difference signal B−Y; first offset providing means for providingan offset for each pixel to the first color difference signal R−Ydepending on the detected hue component for each pixel; and secondoffset providing means for providing an offset for each pixel to thesecond color difference signal B−Y, thereby correcting a hue only for anarbitrary hue, wherein the hue detecting means comprises a first bitshift circuit to which the first color difference signal (R−Y) isinputted, a second bit shift circuit to which a second color differencesignal (B−Y) is inputted, and means for outputting for each pixel huevalues corresponding to output values of both the bit shift circuits ashue components on the basis of a look-up table, and each of the bitshift circuits cutting the number of bits composing an n-bit inputsignal to m which is smaller than n, cutting, when at least therespective uppermost bits in the color difference signals are both zero,the upper x bits in each of the color difference signals, letting x bethe smaller one of the number of bits, out of the bits from theuppermost bit to the (m+1)-th bit in one of the color differencesignals, which are continuously zero from the uppermost bit and thenumber of bits, out of the bits from the uppermost bit to the (m+1)-thbit in the other color difference signal, which are continuously zerofrom the uppermost bit, and further cutting the lower (n−m−x) bits ineach of the color difference signals when x is smaller than (n−m). 4.The hue correcting circuit according to claim 3, wherein an offset isset for each hue, each of the offset providing means comprisingsaturation detecting means for detecting saturation for each pixel fromthe first color difference signal R−Y and the second color differencesignal B−Y, offset calculating means for calculating for each pixel anoffset corresponding to the hue component for each pixel detected by thehue detecting means on the basis of the set offset for each hue, offsetproducing means for multiplying the offset for each pixel calculated bythe offset calculating means by the saturation of the correspondingpixel detected by the saturation detecting means, to produce for eachpixel the offset corresponding to the saturation, and means forproviding for each pixel the offset for each pixel produced by theoffset producing means to the color difference signal.